A device of this type is known from DE-GM 1 886 883. In this document, there is merely proposed as a support only a screen mesh with a coarser wire diameter. This drum covering has the advantage that the perforated drum, or more precisely the material lying thereon, can be more uniformly ventilated than in the case of a simple perforated sheet metal drum. The material for treatment, because of the additional screen mesh, lies at a larger distance from the drum jacket, so that no dead areas, and no areas which are not infiltrated with treatment medium occur over the surface of the material being treated.
It has become apparent in practice, that particularly in the case of extreme drum lengths and even with small drum diameters, the surface stresses arising on the drum, also depending on the density of the material to be treated, have an effect on the precision of rotation of the drum. Irrespective of whether a screen mesh is used or not, or whether a double screen mesh is used, during operation of the drum, the drum metal bulges and thus reduces the previously generated precise rotation of the drum. It has been thought the screen drum with this type of sheet metal construction is not suitable because of such surface stresses.